"When the Vespasians were emperors and censors, in the year from its building 827, the circumference of the Mœnia 'boundary' reckoned thirteen miles and two fifths. Surrounding as it does the seven hills, the city is divided into fourteen districts, with two hundred and sixty-five cross-roads, under the guardianship of the Lares. The space is such that if a line is drawn from the mile column placed at the head of the Forum to each of the gates, which are at present thirty-seven in number, so that by that way enumerating only once twelve gates, and to omit the seven old ones, which no longer exist, the result will be a straight line of twenty miles and seven hundred and sixty-five paces. But if we draw a straight line from the same mile column to the very last of the houses, including therein the Prætorian encampment, and follow throughout the line of all the streets, the result will then be something more than seventy miles." The gates may thus be analyzed:-- 3 in Roma Quadrata } 4 in City of Two Hills } the 7 old ones to be omitted. 18 in the Agger of Servius Tullius. 12 double--that is, 12 in the outer boundary built over the roads where they crossed the Pomœrium, corresponding with twelve in the line of Servius, thus making in all,-- 37, as mentioned by Pliny. Of the twelve gates in the outer boundary, eight still remaining are composed of work of an earlier date than the Wall of Aurelian. The twelve may thus be named: the four gates of the Prætorian camp (two of these partially remain, showing brick-work of Tiberius), Porta Chiusa or Viminalis, Tiburtina, Esquilina now Maggiore, Lateranensis, Latina, Appia, Ardeatina, Ostiensis. Pliny (iii. 9) tells us that Tarquinius Superbus raised an outer agger on the eastern side of Rome. Traces of this still remain, and the tufa stones have been reused in Aurelian's work, whilst the Porta Chiusa is partly formed on the inside of these blocks, and was probably the work of the last of the Tarquins. The Porta S. Lorenzo, or Tiburtina, bears inscriptions of Augustus and Vespasian; Porta Maggiore, of Claudius, Vespasian, and Titus; whilst Porta Lateranensis and Porta Ardeatina were undoubtedly built, as the construction shows, by Nero; and the inner arch of the Porta S. Paolo, or Ostiensis, is of the time of Claudius. Tacitus (xii. 23) says: "The limits of the city were enlarged by Claudius. The right of directing that business was, by ancient usage, vested in all such as extended the boundaries of the empire. The right, however, had not been exercised by any of the Roman commanders (Sylla and Augustus excepted), though remote and powerful nations had been subdued by their victorious arms." "With regard to the enlargement made by Claudius, the curious may be easily satisfied, as the public records contain an exact description" (xii. 24). ROMAN CONSTRUCTION.